Computers are widely used in both business and personal settings. Frequently, the utility of a computer is greatly enhanced by its ability to send or access data over a network. Unfortunately, expanding the functionality of a computer by connecting it with devices operated by other legitimate users also creates the risks that the computer will become connected to devices operated by third parties that may, either unintentionally or maliciously, take actions that cause damage to the computer or the data that it stores. Alternatively, using the network, a third party may improperly gain access to information stored on the computer that was intended to be secret. In these scenarios, rather than enabling desired functionality, the network connection poses a security risk for a computer and its user.
To combat security risks posed by network connections, firewalls are frequently used. A firewall may be a hardware or software component that filters network traffic so that communications with unauthorized third parties are blocked but legitimate network functions may be carried out. Frequently, the filters applied by a firewall are specified by a set of rules defining characteristics of network messages that either should pass through the firewall or that should be blocked.